Facies model of flood basin meandering stream former channel filled with sediments point bar deposits natural levee ,∷ Crevasse clay ::,gravelly sand natural levee (fining upwards sequence) sandy clay/fine sand gravel (channel lag) crevasse-deposits sand with some lateral accretion surfaces older deposits gravel Block diagram of a meandering river
Facies model of meandering stream
Secondary flow refers to small component of flow velocity directed perpendicular to flow A Top diagram shows near-surface near bed velocity vectors A Near-surface secondary flow 4 Near-bed secondary flow A This diagram shows only the secondary components of velocity vectors
Velocity vectors
Vertical variations in point bar deposits Disrupted by burrow/s, = rooting, dessication cracks Small-scale cross-stratificatlon Large-scale cross-stratification Mud Sand
Fining upward Vertical variations in point bar deposits
Lateral variations in point bar deposits Cross-section perpendicular to flow: BIotcTbateu, dessicalIcnFsrackec mud Seals:alc crsc sfialiRed sand Chia'IIEI il dEposi.s ) Gare- scale cross stialifitsa2so-s Note basal erosion surface and lag deposit. Also note bedding geometry in bar deposit: lateral accretion beds dipping tonight, formed from lateral accretion on point bar ithin lateral accretion beds, paleocurrents are directed out of the outcrop, if the outcrop is oriented perp endicular to flow Channel fill deposits consist of fining upward sediments in beds conformable with channel, formed by vertical accretion
Lateral variations in point bar deposits
Braided alluvial sediments: basic vertical sequence with binary 2 m structures of coarse-and fine- grain units but the fine is less than the coarse in thickness Abandoned channel Sand deposition Mud deposition sequence In active in abandoned braided channels channel Active channel sequence 2.3 Physiography and sediments of a braided alluvial channel system. After Selley( 1978)
Braided alluvial sediments: basic vertical sequence with binary structures of coarse- and finegrain units, but the fine is less than the coarse in thickness